The renal sexual segment of the rattlesnake Crotalus durissus (Linneaus, 1758): seasonal cycle and androgen responsiveness

The renal sexual segment of the kidney (RSS) comprises the distal region of the nephron and can be found in many male Squamata reptiles. The RSS has a simple epithelium and the cells are characterized by the presence of sexual granules throughout the cytoplasm. It has been proposed that the secretions are involved with nutrition and activation of spermatozoa in the semen. Several studies on snakes confirmed that the RSS has a seasonal cycle and the hypertrophy of the segmen is related with the mating season. The rattlesnake (Crotalus durissus), a neotropical snake from the Viperidae family, is reproductively active from the late summer to the beginning of the winter in the southeastern Brazil. In this species, the spermatogenic activity starts in the spring, reaching a peak in the summer. Testicular regression has been observed since the fall until the winter. Hence, the present study was address to investigate the renal sexual segment cycle along the four seasons and the androgen responsiveness as well. Forty eight adult males were collected along the four seasons of the year (CEUA-UFMG protocol number 130/2015). The specimens were pre-anesthetized with dry ice, and euthanized with an overdose of barbiturate (thiopental 100 mg/kg) via intra-cardiac. Kidneys and testis were collected, weighed and fixed in Bouin solution. Samples were dehydrated in a sequence of alcohol and embedded in glycol methacrilate for histomorphometric evaluation, and in paraplast for histochemical (Periodic Acid Schiff - PAS and Bromophenol Blue) and immunohistochemical analysis (androgen receptor - AR). The slides were photographed and morphometry was performed using Image J Software. The preliminary results indicate a seasonal cycle of the RSS which is probably related to the seasonal variation of testicular activity. We observed an increase of RSS parameters (kidney-somatic index, tubular diameter, and epithelium height of the RSS) during the summer and fall when compared to the spring and winter. There were also significant differences in the nuclear diameter between the seasons. We observed the highest values for this parameter during the summer and the lowest values in the spring. These results indicate a higher activity of synthesis of the cells of RSS during the summer (before mating season), and the lower activity during the spring. RSS tubules were weakly reactive to PAS and Bromophenol Blue during the spring, showing low concentrations of glycidic and proteinaceous compounds. RSS lower activity in the spring would be associated to returning of the spermatogenesis, since the testes were regressed in the winter. PAS and Bromophenol Blue positive tubules predominate in the summer (before mating season), fall (mating season) and winter. The highest values of the gonadossomatic index in the summer correspond to the peak of spermatogenesis, and the lowest values found in the winter correspond to the testes regressed. Hypertrophy of the RSS in the winter is possibly related to the extended breeding season and/or opportunistic copulation. The early regression of RSS in the winter is observed, however, strong PAS and Bromophenol Blue reaction was maintained probably due the reduction of RSS tubules volume. AR positive cells were found in the RSS during the spring. Taken together, the results suggest that the RSS undergoes remarkable changes along the year and these functional modifications observed might be modulated by androgens. Further studies are being developing in order the better understand these mechanisms.